Automatic adjustment of freely running clocks by line-transmitted or wireless time information is well known from the prior art. Time data, which are modulated onto a continuous carrier signal with definable allocation of the reference time, is referred to subsequently as time information.
Known examples of such time information are the time signals that have already been broadcast for several decades, which fill up a stipulated time grid with variable and modulated symbols. The time reference of the transmitted time information is given by the time grid. Examples are DCF77 in Germany, MSF in Great Britain and WWV, WWVH, WWVB in the USA. Details concerning these are provided in the following publications:    A. Bauch, P. Hetzel, D. Piester, “Time and Frequency Dissemination with DCF77: From 1959 to 2009 and beyond” PTB-Mitteilungen, Special Issue Vol. 119, No. 3, pp-3-26, available at:    http://www.ptb.de/cms/fileadmin/internet/publikationen/ptb_mitteilungen/mitt2009/Heft3/PTB-Mitteilungen_2009_Heft_3_en.pdf (Jan. 28, 2016)    Piester, D., Bauch, A., Becker, J., & Hoppmann, A.: “Time and Frequency Broadcast with DCF77”, Proc. 43rd Precise Annual Time and Time Interval (PTTI) Systems and Applications Meetings (pp. 185-196), available at:    https://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abteilung_4/4.4_zeit_und_frequenz/pdf/2012_Piester_ProcPTTI2011.pdf (Dec. 22, 2015)    “NPL Time & Frequency Services—MSF 60 kHz Time and Date Code”, available at: http://www.npl.co.uk/upload/pdf/MSF_Time_Date_Code.pdf (Nov. 24, 2015)    “NIST Time and Frequency Radio Stations: WWV, WWVH, and WWVB”, NIST Special Publication 250-67, available at: http://tfnist.gov/general/pdf/1969.pdf (Nov. 24, 2015)    J. Lowe: “Enhanced WWVB Broadcast Format, Time and Frequency Services”, National Institute of Standards and Technology, Revision 1.01, Nov. 6, 2013, available at: http://www.nist.gov/pml/div688/grp40/upload/NIST-Enhanced-WWVB-Broadcast-Format-1_01-2013-11-06.pdf (Nov. 18, 2015)    J. Lowe et alt.: “New Improved System for WWVB Broadcast”, 43rd Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting, available at: http://129.6.13.54/pml/div688/grp40/upload/Bin-2591.pdf (Nov. 18, 2015)
Further examples for time information broadcasting are multiple source global navigation satellite systems such as the American Global Positioning Service (GPS), Russian GLONASS, and European Galileo. Details about coding and formats of GPS messages are described in:    “Global Positioning System Standard Positioning Service Signal Specification, 2nd Edition, 1995, available under: http://www.gps.gov/technical (January 2016)
One of the problems associated with GPS is GPS spoofing in which false global positioning and time signals are broadcast and overpower authentic ones in a navigation system. Similar attacks of broadcasting false time signal by overpowering the authentic time signal in the vicinity of the time signal receiver under attack can be possible also in other wireless time information broadcasting systems.
Another known example for time information broadcasting are the time telegrams transmitted in packet oriented mode, which are used, among other things, for synchronization of receivers in ripple control technology during operation of electrical grids. Ripple control technology permits network operators to control consumers and/or supply systems. For example, the network operator can selectively influence decentralized supply systems, such as solar, wind and hydroelectric power systems, by ripple control telegrams for purposes of load curve control. Ripple control telegrams can be line-transmitted via communication networks, the power grid or wirelessly via radio. Wirelessly transmitted ripple control telegrams are referred to as radio ripple control telegrams. Europaeische Funk-Rundsteuerung GmbH [European Radio Ripple Control] makes such a wireless transmission channel available via a long-wave transmitter. In addition to the radio ripple control telegrams, time telegrams for time synchronization of receivers are also broadcast via this transmitter. Document U.S. Pat. No. 7,995,963 B2 is referred to for additional details, which discloses a radio ripple control system for controlling a number of decentralized customer terminal devices as a function of customer initiated transmission requests by means of central long-wave transmitters.